An apparatus and method for controlling the flow of a slurry is provided which includes using a constrictor valve on a mixing and dispensing apparatus. The constrictor valve includes a first guide plate and a second guide plate that are spaced a distance apart along the length of the conduit. Extending between the two guide plates, a plurality of elongate members have first and second ends engaged on the first and second guide plates. Upon rotation of at least one of the first and second guide plates, the elongate members are configured to impart pressure on, and constrict the conduit.